Microneedles are known to be used for administration of drugs such as vaccines into the body. The microneedle includes a needle-shaped projection, and the projection has a length that does not reach nerve cells in the dermis layer of the skin. Accordingly, in the administration method using a microneedle, a skin puncture pain can be reduced compared with an administration method using an injection needle. Further, in the administration method using a microneedle, a drug is delivered into the intradermal layer of the skin which is abundant in antigen presenting cells. Accordingly, there is a possibility that the dose of drug can be reduced compared with the subcutaneous drug administration using an injection needle.
In drug administration using a microneedle, a puncture depth of the projection is controlled to a predetermined depth. However, since the projection has the length smaller than that of an injection needle, the projection may not be punctured into a desired depth due to deformation of the skin when the projection is merely pressed against the skin. Accordingly, an injection instrument having a limiter for controlling the depth of puncture into the skin by the projection and a stabilizer that surrounds the projection and reduces deformation of the skin around the projection may be used for microneedle puncture (for example, see PTL 1).